2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 3
Presentation Time: 1:30 PM-5:30 PM


KNAPP, Elizabeth, PONTIER, Laura and GREEN, Katie, Geology, Washington and Lee University, Lexington, VA 24450, knappe@wlu.edu

Rockbridge County, Virginia is located in the Maury River watershed, an upper Chesapeake Bay tributary. The valley is underlain by Cambrian and Ordovician carbonates. Land use is primarily agricultural and groundwater (including springs) is the major drinking water source. Previous research has indicated a relationship of land use to elevated nitrate in some county streams, several municipal wells have been taken offline recently due to bacterial contamination from surface water influence, and droughts in recent years have impacted many homeowners' water supplies. Large springs in the county have flows upwards of 5,000 gpm and have been investigated for commercial bottling purposes. Concern about the continued quality and quantity of the county's groundwater resources prompted the formation of a Groundwater Steering Committee including a partnership with the local USDA Soil and Water Conservation District.

A geochemical survey of the springs within the drainage basin was initiated in 2004. The goals for this ongoing project have included evaluating flow in order to determine recharge area of individual springs, using geochemical signatures to determine source aquifers, creating a database and website of the spring inventory for public information, and using water chemistry to understand basin-wide carbonate weathering chemistry.

To date, 29 of the county's major springs within 11 distinct geologic units have been studied. Measurements have included GPS location, flow of the source, pH, conductivity, temperature, alkalinity, and major and trace composition. The geology of the spring locations was determined and representative rock samples were analyzed for major and trace elements. A relationship between the elemental composition of spring waters and their possible source rock has been observed and continued work will further explore the potential of using spring geochemistry as a tool for tracking groundwater resources within the watershed.